1. Field of the Invention
The present invention relates generally to a cathode ray tube device. More specifically, this invention relates to a cathode ray tube device with reduced beat noise caused by vibration generated in coils around a deflection yoke due to an alternating current flowing therein.
2. Related Background Art
Recently, display monitors have been increasingly improved in flatness and increased in size; such trends require strict convergence properties. On the other hand, with the spread of software that allows the information to be displayed at the periphery of a screen, users have been requesting very high levels of convergence properties.
Conventionally, magnetic fields generated by horizontal and vertical deflection coils of a deflection yoke have been controlled and adjusted so as to reduce misconvergence that mainly attributes to variations caused during assembly. This alone, however, hardly makes it possible to exclude misconvergence and therefore, a convergence correction unit or a distortion correction unit (a saturable reactor) is used for the purpose of controlling impedance of the deflection yoke to reduce misconvergence.
The convergence correction unit is housed in a two-part resin case 7 as shown in FIGS. 12A and 12B. The configuration of the convergence correction unit includes, as shown in FIG. 13, a control coil 1 connected in series with a vertical deflection coil and controlled coils 3 wound around four drum cores 5 disposed in pairs on both sides of the control coil 1, respectively. Magnets 6 magnetized in the thickness direction are attached to both outer sides of the drum cores 5 to apply a magnetic bias to the controlled coils 3. When a vertical deflection current flows therein, the control coil 1 vibrates, and thus beat noise is generated among the lead wires constituting the control coil 1, between the drum cores 5 and the lead wires, or between the control coil 1 and the case 7.
With regard to this beat noise, for instance, JP8-329859A discloses a method of reducing beat noise, wherein as shown in FIG. 13, a control coil 1 and controlled coils 3 are fixed to a case 7 through an adhesive 131 such as a silicone adhesive, so that the control coil 1 is kept out of contact with the case 7.
Although, this method can suppress the beat noise generated between the control coil 1 and the case 7, it cannot reduce directly the vibration of the noise source itself, namely, the control coil 1. Accordingly, it was not possible to suppress the beat noise generated by interference among lead wires or between the lead wire and a drum core 4.
Furthermore, the use of the adhesive 131 increases material and processing costs, which has been another disadvantage.
This invention is intended to solve such conventional problems as mentioned above. It is an object of the present invention to provide a cathode ray tube device in which vibration of a noise source itself such as a control coil is reduced by a simple and inexpensive method, and thus less beat noise is caused.
This invention achieves an improvement in a cathode ray tube device including: a cathode ray tube with an envelope composed of a panel having a phosphor screen on its inner face and a funnel having a neck portion provided with an electron gun; and a deflection unit having a plurality of coils and disposed around an outer surface of the funnel. In order to achieve the above-mentioned object, at least one of the coils of the deflection unit is provided with an inductance-adjusting element for reducing an inductance of the coil at a frequency in an audio frequency band so as to reduce noise that is generated by the coil whose inductance is thus reduced.
This configuration allows vibration of the control coil itself as a beat noise source to be reduced, and thereby, beat noise at a frequency of 200 Hz or higher can be reduced without using an adhesive such as a silicone adhesive.
In the above-mentioned configuration, the inductance-adjusting element can be a closed-loop coil that is coupled magnetically to the at least one of the plurality of coils included in the deflection unit and includes at least one turn of conductor. Thus, beat noise can be reduced by a simple and inexpensive method in which the closed-loop coil for beat-noise reduction is added.
In this configuration, the deflection unit can include a deflection yoke including a horizontal deflection coil and a vertical deflection coil, and auxiliary coils through which a current is passed in synchronization with a deflecting current. In the deflection unit, at least one of the horizontal deflection coil, the vertical deflection coil and the auxiliary coils can be coupled magnetically to the closed-loop coil.
With respect to the auxiliary coil, the auxiliary coil includes control coils of a convergence correction unit disposed on a side of the electron gun of the deflection yoke and connected in series with the horizontal deflection coil or the vertical deflection coil.
Furthermore, the auxiliary coil can include the control coil wound around a drum core and at least one pair of two-part controlled coils disposed on both sides of the control coil, and each of the two-part controlled coils is wound around drum cores other than the above-mentioned drum core around which the control coil is wound.
The aforementioned respective configurations allow the vibration of coils as beat noise sources other than a control coil to be reduced, and thus beat noise at a frequency of 200 Hz or higher can be reduced without using an adhesive such as a silicone adhesive.